We're running Internet presenses on behalf of quite a few other companies,
and I've come across an issue I don't think has an easy answer.

Running squid as our proxy cache is great, but it doesn't realise all
these other domains are local too unless I explicitly tell it - and as we
add domains regularly, I don't want to be editing squid.conf
continually... All these domains are in only a few IP address ranges, so
I could configure squid by IP address - but then doesn't that add a large
DNS-lookup overhead? I'm not sure on that point as we are the primary NS
for these domain - so all lookups are local - but I thought I'd ask.